Fair simulation

The simulation preorder for labeled transition systems is defined locally as a game that relates states with their immediate successor states. Liveness assumptions about transition systems are typically modeled using fairness constraints. Existing notions of simulation for fair transition systems, however, are not local, and as a result, many appealing properties of the simulation preorder are lost. We extend the local definition of simulation to account for fairness: system S fairly simulates system I iff in the simulation game, there is a strategy that matches with each fair computation of I a fair computation of S. Our definition enjoys a fully abstract semantics and has a logical characterization: S fairly simulates I iff every fair computation tree embedded in the unrolling of I can be embedded also in the unrolling of S or, equivalently, iff every Fair-AFMC formula satisfied by I is satisfied also by S (AFMC is the universal fragment of the alternation-free -calculus). The locality of the definition leads us to a polynomial-time algorithm for checking fair simulation for finite-state systems with weak and strong fairness constraints. Finally, fair simulation implies fair trace-containment, and is therefore useful as an efficientlycomputable local criterion for proving linear-time abstraction hierarchies.